To assemble a wind turbine, generally the wind turbine tower is first secured to a foundation, and a nacelle is then hoisted into place and secured to the tower. In a final assembly step, the rotor blades are hoisted into place and mounted to a hub at the front of the nacelle. To lift these heavy components into place, a suitable crane construction is used, and the load is suspended from a lifting cable. Generally, some kind of gripping means or lifting frame may be used to grip the heavy component during lifting, and the gripping means with load is suspended from a lifting hook on the lifting cable. A problem associated with the assembly procedure is that the components must be lifted to a considerable height, particularly in the case of large generators, since these are generally also mounted on top of very high towers. A tower height in excess of 100 m is no longer the exception. Furthermore, the components themselves are very heavy. A large generator, with a correspondingly large number of magnet poles and stator coils may weigh in excess of 330 metric tons. Similarly, the rotor blades of a large generator may be very long, and may be 50-80 m or more in length. Lifting such large, heavy and unwieldy components can be made even more difficult if weather conditions are unfavorable, since the heavy load is essentially only suspended from a single lifting cable. Wind gusts can cause the load to swing and become dangerously unstable. Therefore, prior art assembly methods may only be carried out in calm weather, which may be rare particularly for offshore wind locations. One approach at dealing with this problem involves arranging a sliding carriage on the crane, and fixing one end of a tag wire to the load. The tag wire passes over the carriage. The carriage can be pulled upwards by a cable connected to a winch. As the load is raised, the carriage is pulled upwards. The tag wire can be held under tension so that a swaying or swinging motion of the load is restricted. However, the effectiveness of this approach is limited, and care must be taken to synchronize the upward motion of the carriage, and the paying out of the tag wire, with the upward motion of the load.